Haitian police demanding better working conditions shot up the army headquarters Sunday, the head of the armed forces said.
Media reports said six people were wounded in the attack in Port-au-Prince.
"We are under siege. We are coming under fire with all kinds of weapons -- assault rifles, Molotov cocktails, tear gas," General Jodel Lessage told AFP.
He said soldiers had returned fire but did not give an injury toll, nor could he say how many people were at the army headquarters, near the presidential palace, at the time of the attack.
For months, Haitian police have been demanding better working conditions, in particular the right to form a union so as to ensure transparency in talks with the police hierarchy.
Last week, some officers took to the street, blocking them and setting fire to cars.
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On Saturday, President Jovenel Moise announced measures designed to ease the crisis, including the creation of a compensation fund for families of police who die in the line of duty and a fund to provide officers with insurance.
Haiti has witnessed a spike in kidnappings for ransom since the beginning of the year and fighting between rival crime gangs, which regularly set up roadblocks on Haitian highways.